阅读说明：本技术 一种数字等报幅cw信号解调方法 (Digital equal-amplitude cw signal demodulation method ) 是由 石玉 贾宇 魏磊 于 2020-06-08 设计创作，主要内容包括：本发明公开了一种数字等报幅cw信号解调方法,涉及数字接收机技术领域,本发明采用数字方式取代传统的模拟电路方式实现CW解调,首先使用数字下变频模块(DDC)去除载波并降低采样率,然后使用高精度直接数字频率合成器(DDS)产生数字拍频器(DBFO)中的本振信号,减少后级数字拍频器(DBFO)的处理压力,从而使用较少的资源获得较高的拍频精度以及较大的拍频范围。(The invention discloses a demodulation method of a digital equal amplitude CW signal, which relates to the technical field of digital receivers and adopts a digital mode to replace a traditional analog circuit mode to realize CW demodulation.)

1. A demodulation method of a digital equal-amplitude cw signal is characterized in that: the method comprises the following steps:

step 1, an intermediate frequency signal (IF) is obtained by processing a radio frequency signal (RF) through a radio frequency module, and the intermediate frequency signal (IF) is converted into a digital signal S through high-speed AD sampling_m(t) digital down conversion module DDC to digital signal S_m(t) carrying out quadrature frequency mixing and then moving the signals to the vicinity of zero frequency to obtain an in-phase signal Mix _ I and a quadrature signal Mix _ Q;

step 2, the in-phase signal Mix _ I and the orthogonal signal Mix _ Q obtained in the step 1 are subjected to data extraction through a cascade comb (CIC) filter, so that the sampling rate is reduced, and high-frequency components caused by the previous-stage mixing are suppressed;

step 3, the signal processed in the step 3 passes through an FIR filter, solves the aliasing problem caused by the reduction of the sampling rate, meets the filtering requirement, and outputs baseband signals FIR _ I and FIR _ Q;

step 4, enabling orthogonal baseband signals FIR _ I and FIR _ Q to enter a digital beat frequency Device (DBFO), wherein the digital beat frequency Device (DBFO) can adjust the baseband signals to any position of +/-fs/2 Hz (fs refers to the sampling rate of input signals), and the used high-precision DDS can ensure that the frequency precision reaches 0.78125 Hz;

and 5, taking out the real part of the complex signal, and outputting the real part as a CW demodulation result.

2. The method for demodulating a digital equal-amplitude cw signal according to claim 1, wherein: in step 1, the generated mixing signals are as follows:

Mix(t)＝cos(ωt)-j*sin(ωt),

the AD sampled signal is:

S_m(t)＝A*cos(ω_ct)，

S_m(t) mix the in-phase signal after mixing:

S_m(t) mix quadrature signals after mixing:

3. the method for demodulating a digital equal-amplitude cw signal according to claim 1, wherein: in step 2, the low-pass characteristic of the cascaded comb (CIC) filter is applied to the high frequency component sin (ω + ω)_c) And cos (ω + ω)_c) Inhibition occurs.

4. The method for demodulating a digital equal-amplitude cw signal according to claim 1, wherein: in step 3, FIR _ I is cos (Δ ω) t, and FIR _ Q is cos (Δ ω) t.

Technical Field

The invention relates to the technical field of digital receivers, in particular to the technical field of a digital equal-amplitude cw signal demodulation method.

Background

The core content of the communication system is modulation and demodulation, and a transmitting end converts a baseband message signal into a required frequency band signal by using a modulation technology so as to transmit the signal in a specific frequency band channel, wherein the demodulation is the inverse process of the modulation and aims to recover the message signal transmitted by the transmitting end. Despite the current emergence of various novel radio communication systems, the conventional communication mode of short-wave communication is still generally regarded by all countries, and especially in military communication, emergency communication and emergency disaster relief, the short-wave communication plays an irreplaceable role. The constant amplitude wave (CW) is a simple and practical communication system in short wave communication. CW is used for demodulation of the morse code, which is a single tone, and a decoding person interprets acquired information according to the length and rhythm of sound. Since different people like different pitches, the sound level, also called beat frequency, can be changed by shifting the spectrum. CW has since been used not only to demodulate morse codes but has become a demodulation mode, and the demodulated signal can be any signal.

With the development of software radio technology and the wide application of large-scale integrated circuits, communication systems gradually begin to adopt a pure digital architecture for processing, and the configurable characteristics of programmable devices can meet different communication function requirements. It is therefore the effort of those skilled in the art to implement CW demodulation in a digital manner instead of in a conventional analog circuit manner.

Disclosure of Invention

The invention aims to: in order to solve the above technical problem, the present invention provides a demodulation method for cw signals with equal digital amplitudes.

The invention specifically adopts the following technical scheme for realizing the purpose:

a demodulation method of a digital equal-amplitude cw signal is characterized in that: the method comprises the following steps:

step 1, an intermediate frequency signal (IF) is obtained by processing a radio frequency signal (RF) through a radio frequency module, and the intermediate frequency signal (IF) is converted into a digital signal S through high-speed ADC sampling_m(t) digital down conversion module DDC to digital signal S_m(t) carrying out quadrature frequency mixing and then moving the signals to the vicinity of zero frequency to obtain an in-phase signal Mix _ I and a quadrature signal Mix _ Q;

step 2, the in-phase signal Mix _ I and the orthogonal signal Mix _ Q obtained in the step 1 are subjected to data extraction through a cascade comb (CIC) filter, so that the sampling rate is reduced, and high-frequency components caused by the previous-stage mixing are suppressed;

step 3, the signal processed in the step 3 passes through an FIR filter, solves the aliasing problem caused by the reduction of the sampling rate, meets the filtering requirement, and outputs baseband signals FIR _ I and FIR _ Q;

step 4, enabling orthogonal baseband signals FIR _ I and FIR _ Q to enter a digital beat frequency Device (DBFO), wherein the digital beat frequency Device (DBFO) can adjust the baseband signals to any position of +/-fs/2 Hz (fs refers to the sampling rate of input signals), and the used high-precision DDS can ensure that the frequency precision reaches 0.78125 Hz;

and 5, taking out the real part of the complex signal, and outputting the real part as a CW demodulation result.

In step 1, the generated mixing signals are as follows:

Mix(t)＝cos(ωt)-j*sin(ωt)，

the AD sampled signal is:

S_m(t)＝A*cos(ω_ct)，

S_m(t) mix the in-phase signal after mixing:

S_m(t) mix quadrature signals after mixing:

in step 2, the low-pass characteristic of the cascaded comb (CIC) filter is applied to the high frequency component sin (ω + ω)_c) And cos (ω + ω)_c) Inhibition occurs.

In step 3, FIR _ I is cos (Δ ω) t, and FIR _ Q is cos (Δ ω) t.

The invention has the following beneficial effects:

the invention adopts a digital mode to replace the traditional analog circuit mode to realize CW demodulation. Firstly, a digital down-conversion module (DDC) is used for removing carriers and reducing the sampling rate, then a high-precision direct digital frequency synthesizer (DDS) is used for generating local oscillation signals in a digital beat frequency Device (DBFO), and the processing pressure of a post-stage digital beat frequency Device (DBFO) is reduced, so that less resources are used for obtaining higher beat frequency precision and a larger beat frequency range.

Drawings

FIG. 1 is a block flow diagram of the present invention;

FIG. 2 is a block diagram of a superheterodyne receiving system;

FIG. 3 is an internal block diagram of a digital beat frequency device;

FIG. 4 is a frequency spectrum of AD acquisition data;

FIG. 5 shows the DDC down-sampled output;

fig. 6 shows the CW demodulated output.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention.